Just tested Alk, it's normal. Usually I just bring a water sample to LFS, everything is fine, was there just couple days ago. I have 72 G tank, 2x150W/20K
MH lights (5 hours a day)
(this is quite a short photo period for SPS, especially considering the lamps are 20K which will usually have a lower photo synthetically available light yeild than lower kelvin light sources such as the 12 or 10K...even then, at 2 x 150W, Id be looking at a photo period of at least 6-8 hours per day with a maximum of 10-12), 24G sump with protein skimmer, also I use canister filter with different media to remove phosphates (clean every week...
Good), 20% water changes with RO/DI water using Instant Ocean salt mix every two weeks
(good), adding "PurpleUp" and Kent Marine "Essential Elements",
(probably not helping much...everything you realy need is in your salt already bar a bit of occasional tweaking with something like C-Balance) There is one hard fast rule of keeping marines...If you cant test for it...you shouldnt add it...temperature 82.
( I think this may be one of your main issues, anything over 80 can be quite stressfull for SPS in closed systems, especially if other perameters are fluctuating out of ideal zones as well...Although in some systems they cope quite well (and in some cases in the wild) there are other aspects that allow the corals to cope with those conditions....For two years I couldn't keep any
SPS for longer then 2 months.
MH Metal Halide Lighting, typically used for high intensity light demanding corals such as SPS. Bulbs come in varieties of spectrums (7k, 10k,20k), and intensity (175W, 250W, 400W).
SPS Small Polyped Scleractinians - Sometimes known as Small Polyped Stony corals. These are hard corals that have extremely small polyps. They are typically on the difficult side and require Metal Halide lighting or dense Power Compact or T5 arrays. These corals are prized for their rareness and ability to be easily fragged into multiple colonies.